A cooling system constructed in the aforementioned manner is disclosed in Patent document 1. Patent document 1 discloses a technique including a flow passage for sending out coolant of an engine to a heater core and a flow passage for sending out the coolant of the engine to a radiator, the aforementioned flow passages being provided separately from each other, and a water pump for returning the coolant of each of the flow passages to the engine. In Patent document 1, a coolant stop valve which is selectively opened and closed is provided at an engine side of the flow passage that sends the coolant to the heater.
The coolant stop valve in Patent document 1 is configured to include a valve body made of a magnetic material and configured to reach a closed state by making contact with a valve seat, a biasing means (spring) applying a biasing force in a direction where the valve body makes contact with the valve seat (in a closing direction) and a solenoid suctioning the valve body by an electromagnetic force so that the valve body makes contact with the valve seat. According to the aforementioned construction, the biasing force of the biasing means that biases the valve body in the closing direction is specified so that the valve body is opened by a pressure of the coolant.
Specifically, in Patent document 1, the flow passage sending out the coolant of the engine to the heater core and the flow passage sending out the coolant of the engine to the radiator are separately provided. Thus, a flow of the coolant to the radiator is secured even in a case where a malfunction such as disconnection occurs at the solenoid to thereby inhibit overheating of the engine.
Patent document 2 discloses a technique including a first flow passage, a second flow passage to each of which cooling water of an internal combustion engine is sent, the first flow passage and the second flow passage being provided separately from each other, and a water pump provided at a common flow passage where the cooling water of the first flow passage and the cooling water of the second flow passage join together so that the water pump returns the cooling water to the internal combustion engine. In Patent document 2, a fluid cooling means (radiator) is provided at the first flow passage for cooling the cooling water. In addition, a heat exchanging means is provided at the second flow passage for receiving heat of the cooling water. A first valve is provided at a joining portion of the first flow passage and the second flow passage. A second valve is serially provided at a position in series with the heat exchanging means at the second flow passage.
In Patent document 2, the first valve, which includes a thermostat, is configured to increase an amount of cooling water flowing through the first flow passage and the second flow passage with an increase of temperature of the cooling water. The second valve is configured as an electrically driven flow control valve which adjusts an amount of cooling water flowing to the heat exchanging means.
In Patent document 2, a first sensor detecting a temperature of the cooling water sent out from the internal combustion engine and a control apparatus controlling the first valve and the second valve are provided. The control apparatus is configured to perform a control for increasing an amount of cooling water flowing through the first flow passage by opening the first valve based on an operation of a heater of the first valve in a case where the control apparatus determines a malfunction of the second valve based on a detection result of the first sensor.